Production of propylene glycol (PG) from glycerin is becoming increasingly attractive relative to traditional hydration of propylene oxide due to the availability of inexpensive glycerin. On the other hand, traditional methods for producing PG from propylene oxide do not produce toxic byproducts, such as ethylene glycol (EG). In contrast, the process for producing PG from glycerin uses a heterogeneous catalyst, which also forms EG.
Particular grades of PG are used in foods and medicine. On the other hand, EG is toxic and harmful to mammals. Traditionally, distillation is used to separate PG and EG. However, due to the similar chemical natures of EG and PG, reduction of EG content to low levels is extremely expensive via conventional distillation. A very large number of stages and very high reflux ratios are used, resulting in high capital and operating costs.
As such, improved techniques for removing EG impurities from PG would be desirable.